Optically monitoring comb-line of escalators and moving walks

ABSTRACT

Method for monitoring at least part of a comb-line ( 18 ) of a comb plate ( 14 ) having a plurality of teeth ( 16 ), of a people conveyor ( 2 ) having a movable transportation band ( 4 ) and the comb plate ( 14 ) located at the transition ( 20 ) between the movable transportation band ( 4 ) and the stationary comb plate ( 14 ), wherein the method includes (a) taking a picture of the comb-line ( 18 ) with a camera ( 12 ); (b) comparing the picture with a reference picture; (c) determining the safety state of the comb-line ( 18 ) based on such comparison.

The present invention relates to the monitoring of at least part of acomb-line of a comb plate having a plurality of teeth, of a peopleconveyor having a movable transportation band and the comb plate whichis located at the transition between the movable transportation band andthe stationary comb plate.

It is known that people conveyor like escalators and moving walkwayshave an endless transportation band which moves along an endless paththrough an exposed area where the transportation band is exposed totransport the passenger, a turnaround area, and a return path as well asa further turnaround area which closes the endless path to the exposedarea. The transportation band can be formed from a plurality ofindividual tread elements like steps and pallet. Alternatively, thetransportation band can be an elastic endless belt.

For security reasons the disappearing area, where the movingtransportation band disappears under the stationary landing area of thepeople conveyor is of highest concern. Particularly, high efforts aretaken to keep the gap between the moving transportation band and thestationary structure as small as possible. To this end, thetransportation band frequently has a cleated surface, while thecorresponding stationary structure has a comb-like shape with theindividual teeth of the comb extending into the groves between adjacentcleats on the transportation band surface. The individual teeth aretapered so as to urge any objects away from the disappearingtransportation band. However, there is the risk of tooth-breaking, forexample the European product standard code requires periodic inspectionand test, to ascertain the proper condition of the comb. Particularly,there are requirements to check the comb plate for a broken tooth once aday and to shut down the people conveyor, once two adjacent teeth arebroken. While this check is typically being performed by operatingpersonnel of the people conveyor, there is a tendency to automaticallyperform monitoring of the teeth of the comb plate. Several approacheshave been suggested for automatically monitoring the comb plate andparticularly monitoring if two adjacent teeth are missing. US2004/0035675 A1 discloses to provide conductors for each individualtooth so that a conductor will break if a tooth breaks. The conductorsare connected to a control unit which allows for assessing if only asingle or two adjacent teeth are broken. DE 102 23 393 A1 suggests, onthe other hand, to monitor the comb plate with a laser distancemeasuring device. Those approaches are relatively complicated andexpensive to implement.

It is the object of the present invention to provide a method and anapparatus for monitoring comb plate teeth which is reliable, easy toinstall with existing installations and cost-efficient.

In accordance with the present invention, this object is solved by thefollowing steps:

-   -   (a) taking a picture of the comb-line with a camera;    -   (b) comparing the picture with a reference picture;    -   (c) determining the safety state of the comb-line based on such        comparison.

Electrical cameras and particularly digital cameras, and imageprocessing units are readily available at relatively low cost. They haveproven to be reliable enough to be used for monitoring the comb plateor, better to say the comb-line, for broken teeth. The method maycomprise taking a picture and making the determination on the basis of asingle picture, for example once or several times a day, for example inthe morning, or before the people conveyor starts operating. It is alsopossible to make the determination on the basis of a plurality ofpictures. It is also possible to take pictures at certain intervals, forexample every hour, every thirty minutes, every second, etc. It is alsopossible to form an image processing on any picture taken beforecomparing it with a reference picture. Image processing can also beperformed only after the comparing step.

The picture-taking step can include taking a plurality of pictures,sampling pictures at intervals or continuously. It is possible tocompare each single picture with a reference picture or tocombine/integrate a plurality of pictures and to compare the integratedpictures with the reference picture.

It is possible to bring out or carve out the static comb-line from thepicture by pattern filtering the picture. The pattern filtering can beperformed by taking into account specific information about thecomb-line, for example orientation of teeth, dimension of teeth, numberof teeth, spacing between teeth, the particularly related section of thepicture, etc.

The step of comparing the picture with the reference picture can includesubtracting the pictures from each other. By doing so the result can bemerely the difference between the pictures, i.e. a missing tooth, etc.It can be preferred to have a reference picture in which the same orcorresponding pattern filtering steps have been performed as the patternfiltering steps performed with the picture taken in order to provide forvery closely corresponding pictures to be compared with each other or besubtracted from each other.

The picture-taking steps can include taking pictures independent of thetraffic situation, which exists on the movable transportation band, andpreferably performing an interference elimination by correlating aplurality of pictures. Alternatively, it is possible to monitor whetherpeople are present on the people conveyor or next to the comb-line andto take pictures only if no people or objects are present.

The interference elimination can comprise autocorrelating a plurality ofindividual comparisons of pictures with the reference picture. By doingso the pictures are first taken and subsequently individually comparedwith the reference picture in the next step, a plurality of individualcomparison results are compared with each other and any temporaryinterference is taken out of consideration. This can be done by not atall using a picture including an interference, but is preferably done byusing only those portions of the picture where there is no interference,i.e. by using the clearly visible portion of the comb plate only.

It is further possible to calculate a stability grade reflecting thereliability of the comparison result after interference elimination andpreferably to determine the safety state only if a required level ofstability grade has been reached.

The reference picture can be a picture which was taken by the camerawhich also takes the pictures to be compared.

The present invention further refers to a comb teeth monitoring devicefor monitoring at least the part of a comb-line of a people conveyorhaving a movable transportation band and a comb plate which is locatedat the transition between the movable transportation band and thestationary comb plate wherein the comb plate has a plurality of teethforming the comb-line, comprising a camera and a memory for storing areference picture of a comb-line, a comparison unit for comparing apicture taken by the camera with a reference picture and a determiningunit for determining the safety state of the comb-line based on thecomparison. The determining unit can be adapted to determine either of asafe or an unsafe condition and can be connected to the people conveyorcontrol so as to stop the people conveyor once an unsafe condition hasbeen determined. It is also possible to stop the people conveyor only ifa subsequent separate test confirms an unsafe condition. It is alsopossible that the determining unit is adapted to provide at least oneadditional warning state between the safe and the unsafe condition, forexample if a single tooth or two teeth, which are not adjacent, arebroken.

The comb teeth monitoring device may further comprise apattern-filtering unit. The comparison unit may comprise a subtractingunit for subtracting the reference picture and the picture taken by thecamera from each other. The comb teeth monitoring device may furthercomprise an interference elimination unit operatively connected to amemory for correlating a plurality of pictures taken by the camera witheach other. The comb teeth monitoring device may further include areference picture button for storing into the memory a picture taken bythe camera. The reference picture button can be a reset button or arefresh button and can be a physical feature of the monitoring deviceitself. Alternatively, it can be connectable to the monitoring device aspart of a service tool like a service laptop, etc.

A further embodiment of the present invention relates to a peopleconveyor having a comb teeth monitoring device as disclosed above. Acamera can be located above and lateral to the comb-line. Preferably,the people conveyor includes a balustrade lateral to the transportationband, wherein the camera is located within the balustrade above andlaterally to the comb-line.

The camera can further be located below the comb plate and the treadelements so that it takes and uses the pictures through the gap betweenadjacent tread elements.

While having a camera located in the balustrade, it is readilyaccessible for maintenance operation, etc., locating the camera belowthe comb plate has the advantage of having the camera securely hiddenagainst vandalism.

Embodiments of the present invention will be described below withrespect to the drawings in which:

FIG. 1 shows a part of a people conveyor embodying the presentinvention;

FIG. 2 a to 2 c schematically show a comb plate without and withdefects;

FIG. 3 schematically shows a comb plate error detection by comparing animage as taken by the camera with a reference picture;

FIG. 4 is a logic diagram showing the monitoring method; and

FIG. 5 is a schematic representation of a comb teeth monitoring device.

FIG. 1 shows a people conveyor 2 having a movable transportation band 4which is formed of a plurality of tread elements 6 arranged one afterthe other leaving a gap 8 between adjacent tread elements 6. The peopleconveyor 2 further comprises a balustrade 10 having a camera 12 of acomb teeth monitoring device located therein. The people conveyor 2further comprises a stationary comb plate 14 with teeth 16 at its endfacing toward the transportation band 4. The teeth 16 and the foremostportion of the comb plate 14 together form the comb-line 18. Thecomb-line 18 forms the transition 20 from the moving transportation band4 to the stationary comb plate 14.

Dashed lines 22 schematically show the dimension of the picture as takenby the camera 12.

FIG. 2 a schematically shows an image of the comb-line 18, clearlyshowing the individual teeth 16 arranged in parallel to each other andwith a predetermined spacing between each other. FIGS. 2 b and 2 c areperspective Figures corresponding to FIG. 2 a with FIG. 2 b, however,showing a missing tooth between the second and fourth teeth 16 ascounted from left to right in FIG. 2 b. Similarly, FIG. 2 c shows acomb-line 18 with an object 24 being trapped between two adjacent teeth.The conditions as shown in FIGS. 2 b and 2 c are merely two exemplarydefect conditions. Other defect conditions are two or more missingteeth, particularly two adjacent missing teeth and an upwardly tiltedcomb plate or a comb-line having the tips of the comb lifted upwards,etc.

FIG. 3 shows the basic concept of subtracting from a reference picture28 a picture 26 of the comb-line 18 as taken by the camera of thecorresponding comb-line 18. As can be seen in picture 30, the result ismerely the lacking tooth 16.

The logic sequence of FIG. 4 explains the monitoring method in moredetail. The camera 12 takes a picture in step 32. The picture taken instep 32 is forwarded to step 34 for performing pattern filtering of therespective picture. The filtering of the pictures can be performed bypattern filtering based on the information as given in the pictureitself. On the other hand, particularly in the present situation suchpattern filtering can be enhanced or facilitated by using particularinformation on the pattern to be recognized in the particular picture athand. For example the parallel orientation of the teeth 16 of thecomb-line 18 can be used for facilitating pattern recognition andpattern filtering. Once the target pattern is recognized in the picture,it is possible to focus on the pattern of interest, i.e. the comb-line18. The focusing can be done by adjusting the orientation of the camera,but preferably it is done by focusing on the relevant portions of thepictures taken by the camera. Particularly it is possible to select avery narrow portion of the picture only and to ignore the remaininginformation on the picture as taken.

As indicated in step 36, it is possible to continuously sample thepictures. In step 38 each individual picture or a combination of aplurality of sampled pictures can be compared with a reference picture,which has been stored in step 40. The comparison in step 38 can forexample be performed by subtracting from the reference picture thepicture as taken, as shown in FIG. 3.

It is possible to take the reference picture with the same camera 12 andto have the reference picture processed in the same way as theprocessing of other pictures taken is performed in steps 32 and 34. If areference picture is selected, for example by the set-Up start button 42in step 44, the respective reference picture can be stored in step 40 ina memory.

In order to allow for a continuous monitoring of the comb-line 18independent of the traffic condition on the transportation band 4, aninterference elimination step will be performed. In accordance with theembodiment shown in FIG. 4, such interference elimination is performedin step 46 where the pictures as taken and as individually compared withthe reference picture in step 38 are automatically correlated with eachother in order to particularly eliminate temporarily appearinginterference like passengers or objects moving on the transportationband. Alternatively it is possible not to perform the interferenceelimination after individually comparing each picture as taken by thecamera 12 with the reference picture, but to perform the interferenceelimination before the comparison with the reference picture isperformed.

In step 48 a so-called stability grade will be calculated, whichindicates the quality of the elimination of the disturbances asperformed. This stability grade will target to a limiting value becausethere is only a limited number of pictures to be expected: either thecomb-line 18 is complete (FIG. 2 a), or one tooth or more teeth aremissing (FIG. 2 b), or an object has jammed into the comb-line 18 (FIG.2 c). The stability grade can be based on the number of pictures to betaken into account. The number of disturbances which have beeneliminated, the number of repetitions of the monitoring process whichconfirm a particular condition, etc. Once the stability grade issufficient, which can be performed in step 50 by comparing thecalculated stability grade with a predetermined value, the result of themonitoring can be released to a decision step 52 or determining step 52which determines the safety state of the comb-line 18. The determinationas made in step 52 can be input to the people conveyor control (notshown) for stopping the conveyor, for indicating a warning signal, forindicating a maintenance signal, etc., or can be directly linked to asupervising office for starting service operation.

It is possible to determine the type of fault as detected e.g. by themethod as shown in FIG. 4 by comparing the pictures as taken with theresult of the comparison in step 38 with fault reference pictures inorder to identify particular fault conditions and to generate an issuedifferent warning or stop information.

FIG. 5 shows a comb teeth monitoring device 54 for monitoring at leastpart of the comb-line 18 of the people conveyor 2. Particularly, thecomb teeth monitoring device 54 comprises a camera 12 and an imageprocessing unit 56. The image processing unit 56 comprises a patternfiltering unit 58, a memory 60, a comparison unit 62. A referencepicture button 42 serves for storing a reference picture in the memory60. An interference unit 64 directly or indirectly through memory 60receives the results from the comparison unit 62 and eliminates anyinterference as discussed above with respect to step 46. A reliabilitycalculation unit 66 provides for sending only reliable information to adetermining unit 68. The output 70 from the determining unit can beinput to the people conveyor control, etc.

1. A method for monitoring at least part of a comb-line of a peopleconveyor having a movable transportation band with a plurality of treadelements and a gap between adjacent tread elements and the comb platelocated at a transition between the movable transportation band and astationary surface, the comb plate having a plurality of teeth, whereinthe method includes: (a) taking a picture of the comb-line with a camerathat is positioned below the comb plate and bringing out the staticcomb-line of the picture by pattern filtering the picture; (b) comparingthe pattern filtered picture with a reference picture; (c) determining astate of the comb-line based on the comparing.
 2. A method according toclaim 1, wherein the picture-taking step includes taking a plurality ofpictures.
 3. A method according to claim 1, wherein the patternfiltering is performed by taking into account specific information aboutthe comb-line.
 4. A method according to claim 3, wherein the specificinformation includes at least one of: orientation of teeth, dimension ofteeth, number of teeth, spacing between teeth or a related section ofthe picture.
 5. A method according to claim 1, wherein the step ofcomparing the pattern filtered picture with the reference pictureincludes subtracting the pictures from each other.
 6. A method formonitoring at least part of a comb-line of a people conveyor having amovable transportation band and the comb plate located at a transitionbetween the movable transportation band and a stationary surface, thecomb plate having a plurality of teeth, wherein the method includes: (a)taking a picture of the comb-line with a camera and bringing out thestatic comb-line of the picture by pattern filtering the picture; (b)comparing the pattern filtered picture with a reference picture; (c)determining a state of the comb-line based on the comparing, wherein thepicture-taking step includes taking a plurality of pictures independentof a traffic situation on the movable transportation band, andperforming an interference elimination by correlating the plurality ofpictures.
 7. A method according to claim 6, wherein the interferenceelimination comprises: comparing each of the plurality of pictures withthe reference picture resulting in a plurality of individualcomparisons; autocorrelating the plurality of individual comparisons bycomparing results of the individual comparisons against each other toidentify any interference in any of the plurality of pictures; andidentifying any of the plurality of pictures that include interferenceresulting from an object in view of the camera when a corresponding oneof the pictures was taken.
 8. A method according to claim 6, includingcalculating a stability grade reflecting the reliability of thecomparison result after interference elimination, and determining thestate only if a required level of stability grade has been reached.
 9. Amethod according to claim 1, wherein the reference picture is a picturetaken by the camera positioned beneath the comb plate.
 10. A comb teethmonitoring device for monitoring at least part of a comb-line of apeople conveyor having a movable transportation band with a plurality oftread elements and a gap between adjacent tread elements and a combplate located at a transition between the movable transportation bandand a stationary surface, wherein the comb plate has a plurality ofteeth forming the comb-line, comprising: a camera positioned below thecomb plate to take a picture of the comb plate through the gap; a memoryfor storing a reference picture of the comb-line; a pattern filteringunit for filtering a picture taken by the camera; a comparison unit forcomparing a picture taken by the camera with the reference picture; anda determining unit for determining a state of the comb-line based on thecomparison of the comparison unit.
 11. A comb teeth monitoring deviceaccording to claim 10, wherein the comparison unit comprises asubtracting unit for subtracting from each other the reference pictureand the picture taken by the camera.
 12. A comb teeth monitoring deviceaccording to claim 10, including an interference elimination unitassociated with the determining unit, the interference elimination unitcorrelating with each other a plurality of pictures taken by the camera.13. A comb teeth monitoring device according to claim 10, including areliability calculation unit operatively connected to the determiningunit.
 14. A comb teeth monitoring device according to claim 10,including a reference picture button associated with at least one of thecamera or the memory for storing a picture taken by the camera into thememory.